This answer may be late reply but it will be useful for seeing this topic in future.
The features of .NET framework 4.5 can be seen in the following link.
To summarize:
Installation
.NET Framework 4.5 does not support Windows XP or Windows Server 2003, and therefore, if you have to create applications that target these operating systems, you will need to stay with .NET Framework 4.0. In contrast, Windows 8 and Windows Server 2012 in all of their editions include .NET Framework 4.5.
- Support for Arrays Larger than 2 GB on 64-bit Platforms
- Enhanced Background Server Garbage Collection
- Support for Timeouts in Regular Expression Evaluations
- Support for Unicode 6.0.0 in Culture-Sensitive Sorting and Casing Rules on Windows 8
- Simple Default Culture Definition for an Application Domain
- Internationalized Domain Names in Windows 8 Apps